Due to the superior serotonin.sub.3 receptor antagonistic action, 6-amino-5-chloro-1-isopropyl-2-(4-methyl-1-piperazinyl)benzimidazole and an acid addition salt thereof (hereinafter they are also referred to as benzimidazole compound) of the formula (1): ##STR1## are known to be useful compounds as antiemetic agents against emesis caused by cancer chemotherapy using cisplatin and the like (Japanese Patent Unexamined Publication No. 17449/1993). Also, it has been already known that a percutaneous preparation containing a benzimidazole compound as an active ingredient exhibits serotonin.sub.3 receptor antagonistic action upon percutaneous absorption of said benzimidazole compound (Japanese Patent Unexamined Publication No. 48258/1995).
However, a percutaneous preparation containing the above-mentioned benzimidazole compound as an active ingredient is unsatisfactory in the stability of the benzimidazole compound, which is the main drug, contained in the preparation.